Voice service processing method and terminal device

ABSTRACT

The present invention provides a voice service processing method and a terminal device. The method includes: sending, by a terminal device, a first message to a network device of a first network, where the first message is used to request a circuit switched fallback CSFB voice service; receiving, by the terminal device, a second message sent by the network device of the first network, where the second message is used to instruct the terminal device to perform network redirection; if the second message carries no frequency information, determining, by the terminal device, a redirection frequency, where the redirection frequency is a frequency supported by a second network; and sending, by the terminal device based on the redirection frequency, a connection request to a network device of the second network, to perform a CS voice service.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/CN2016/077871, filed Mar. 30, 2016, which is hereby incorporated byreference in their entireties.

TECHNICAL FIELD

Embodiments of the present invention relate to the communications field,and more specifically, to a voice service processing method and aterminal device.

BACKGROUND

With further evolution of wireless communications technologies,currently, a wireless communications system has evolved into the fourthgeneration mobile communications system (Fourth Generation MobileCommunications Systems, “4G” for short). However, 4G does not supportrunning of a circuit switched (Circuit Switch, “CS” for short) service.Therefore, after 4G is deployed in a wireless network, a currentmainstream voice solution is circuit switched fallback (Circuit SwitchedFallback, “CSFB” for short). That is, after a 4G calling user or calleduser receives a paging message, a terminal device falls back to thethird generation mobile communications system (Third Generation MobileCommunication Systems, “3G” for short) or the second generation mobilecommunications system (Second Generation Mobile Communication Systems,“2G” for short), to perform a voice service, and fast returns (FastReturn, “FR” for short) to 4G after the voice service is ended. However,when the existing CSFB solution is used, a 4G mobileoriginating/terminating call is often disconnected. This affects mobilephone communication experience of a user.

SUMMARY

The present invention provides a voice service processing method and aterminal device, so that when the terminal device needs to perform avoice service, even if the terminal device receives no frequencyinformation delivered by a network, the terminal device can determine anappropriate redirection frequency, and access, based on the redirectionfrequency, a network that supports the voice service, to answer a callor make a call. Therefore, voice communication experience of a user isimproved.

For ease of understanding embodiments of the present invention, anelement that is used in description of the embodiments of the presentinvention is first described herein.

In terms of circuit switched fallback (Circuit Switched Fallback, “CSFB”for short), after accessing a network that does not support a CSservice, when a terminal device needs to perform a CS service, theterminal device falls back to a network that supports a CS service fromthe network that does not support a CS service. For example, afteraccessing a 4G network, when the terminal device needs to perform voicecommunication, the terminal device needs to fall back to a 2G or 3Gnetwork.

According to a first aspect, a voice service processing method isprovided, where the method includes: sending, by a terminal device, afirst message to a network device of a first network, where the firstmessage is used to request a circuit switched fallback CSFB voiceservice; receiving, by the terminal device, a second message sent by thenetwork device of the first network, where the second message is used toinstruct the terminal device to perform network redirection; if thesecond message carries no frequency information, determining, by theterminal device, a redirection frequency, where the redirectionfrequency is a frequency supported by a second network; and sending, bythe terminal device based on the redirection frequency, a connectionrequest to a network device of the second network, to perform a CS voiceservice.

In the embodiments of the present invention, the first network may be anetwork that supports only a packet switched (Packet Switch, “PS” forshort) service but does not support a CS service, for example, a 4G LongTerm Evolution (Long Term Evolution, “LTE” for short) network. Thesecond network is a network that supports a CS service, for example, a2G network or a 3G network.

Therefore, according to the voice service processing method in theembodiments of the present invention, when the terminal device needs toperform a voice service, even if the terminal device receives nofrequency information delivered by a network, the terminal device candetermine an appropriate redirection frequency, and access, based on theredirection frequency, a network that supports the voice service, toanswer a call or make a call. Therefore, voice communication experienceof a user is improved.

With reference to the first aspect, in a first possible implementationof the first aspect, the determining, by the terminal device, aredirection frequency includes: obtaining, by the terminal device, firsthistorical frequencies, where the first historical frequencies arefrequencies that are used before the terminal device determines theredirection frequency and that are used to access the second network bythe terminal device in a process in which the terminal device is handedover from the first network to the second network; and determining, bythe terminal device, one of the first historical frequencies as theredirection frequency.

Optionally, the terminal device may save, in each successful CSFBprocess, a frequency that is used by the terminal device to performfallback in this CSFB process. Then, even if the terminal devicereceives no frequency information delivered by the network device, theterminal device can select, from saved frequencies, a frequency that isto be used during fallback. Therefore, time consumed for a fallbackprocess can be reduced, and the voice communication experience of theuser can be improved.

It should be noted that there may be one or more first historicalfrequencies, and generally, there are a plurality of first historicalfrequencies.

With reference to the first aspect, in a second possible implementationof the first aspect, the determining, by the terminal device, aredirection frequency includes: obtaining, by the terminal device,second historical frequencies, where the second historical frequenciesare frequencies that are used before the terminal device determines theredirection frequency and that are used to access the second network byanother terminal device in a process in which the another terminaldevice is handed over from the first network to the second network; anddetermining, by the terminal device, one of the second historicalfrequencies as the redirection frequency.

It should be noted that there may be one or more second historicalfrequencies, and generally, there are a plurality of second historicalfrequencies.

With reference to the second possible implementation of the firstaspect, in a third possible implementation of the first aspect, alocation area of the another terminal in the process in which theanother terminal device is handed over from the first network to thesecond network is the same as a current location area of the terminaldevice.

Therefore, the terminal device can directly obtain a frequency that canbe used to perform fallback in the current location area, so that afallback success rate can be improved, time consumed for a fallbackprocess can be reduced, and the voice communication experience of theuser can be improved.

With reference to the second or the third possible implementation of thefirst aspect, in a fourth possible implementation of the first aspect,the obtaining, by the terminal device, second historical frequenciesincludes: receiving, by the terminal device, the second historicalfrequencies sent by a cloud server.

Optionally, the terminal device may establish device-to-device (Deviceto Device, “D2D” for short) communication with another terminal device,to receive a historical frequency that is saved and sent by the anotherterminal device.

Alternatively, the terminal device may perform information transmissionwith another terminal device by using Bluetooth, to receive a historicalfrequency that is saved and sent by the another terminal device.

Therefore, when the terminal device receives no frequency informationdelivered by the network device, the terminal device can select, fromfrequencies that are used to access the second network by anotherterminal device in the process in which the another terminal device ishanded over from the first network to the second network, a frequencythat is to be used during fallback. Therefore, the frequency that is tobe used during fallback can be determined more quickly, time consumedfor a fallback process can be reduced, and the voice communicationexperience of the user can be improved.

With reference to any one of the first aspect or the first to the fourthpossible implementations of the first aspect, in a fifth possibleimplementation of the first aspect, the method further includes: saving,by the terminal device, a correspondence between the first network andthe redirection frequency.

With reference to any one of the first aspect or the first to the fifthpossible implementations of the first aspect, in a sixth possibleimplementation of the first aspect, the first network is a 4G network,and the second network is a 2G network.

Currently, a coverage area of the 2G network is wider than a coveragearea of the 3G network. Therefore, during circuit switched fallback, theterminal device preferentially chooses to fall back to the 2G network.In this way, network configuration and optimization can be simplified.

According to a second aspect, a terminal device is provided, where theterminal device is configured to perform the method in the first aspector any possible implementation of the first aspect. Specifically, theterminal device includes units configured to perform the method in thefirst aspect or any possible implementation of the first aspect.

According to a third aspect, a terminal device is provided, where theterminal device includes a processor, a memory, and a transceiver, wherethe processor, the memory, and the transceiver are connected by using abus system, the memory is configured to store an instruction, thetransceiver is controlled by the processor to receive and send amessage, to implement communication between the terminal device and anetwork device, and the processor is configured to invoke theinstruction stored in the memory, to perform the method in the firstaspect or any possible implementation of the first aspect.

According to a fourth aspect, a computer readable medium is provided,where the computer readable medium is configured to store a computerprogram, and the computer program includes an instruction used toperform the method in the first aspect or any possible implementation ofthe first aspect.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly describes the accompanyingdrawings required for describing the embodiments of the presentinvention. Apparently, the accompanying drawings in the followingdescription show merely some embodiments of the present invention, and aperson of ordinary skill in the art may still derive other drawings fromthese accompanying drawings without creative efforts.

FIG. 1(a) and FIG. 1(b) are application scenario diagrams according toan embodiment of the present invention;

FIG. 2 is a schematic flowchart of a voice service processing methodaccording to an embodiment of the present invention;

FIG. 3 is another schematic flowchart of a voice service processingmethod according to an embodiment of the present invention;

FIG. 4 is a schematic block diagram of a terminal device according to anembodiment of the present invention; and

FIG. 5 is a schematic block diagram of a terminal device according toanother embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The following clearly and completely describes the technical solutionsin the embodiments of the present invention with reference to theaccompanying drawings in the embodiments of the present invention.Apparently, the described embodiments are some rather than all of theembodiments of the present invention. All other embodiments obtained bya person of ordinary skill in the art based on the embodiments of thepresent invention without creative efforts shall fall within theprotection scope of the present invention.

The technical solutions in the embodiments of the present invention maybe applied to various communications systems, for example, a GlobalSystem for Mobile Communications (Global System of Mobile Communication,“GSM” for short) system, a Code Division Multiple Access (Code DivisionMultiple Access, “CDMA” for short) system, a Wideband Code DivisionMultiple Access (Wideband Code Division Multiple Access, “WCDMA” forshort) system, a Long Term Evolution (Long Term Evolution, “LTE” forshort) system, an LTE frequency division duplex (Frequency DivisionDuplex, “FDD” for short) system, an LTE time division duplex (TimeDivision Duplex, “TDD” for short) system, a Universal MobileTelecommunication System (Universal Mobile Telecommunication System,“UMTS” for short), and a future 5G communications system.

In the embodiments of the present invention, a terminal device (TerminalEquipment) may also be referred to as user equipment, a mobile station(Mobile Station, “MS” for short), a mobile terminal (Mobile Terminal),or the like. The user equipment may communicate with one or more corenetworks by using a radio access network (Radio Access Network, “RAN”for short). For example, the user equipment may be a mobile phone (orreferred to as a “cellular” phone), or a computer with a mobileterminal. For example, the user equipment may be a portable,pocket-sized, handheld, computer built-in, or in-vehicle mobileapparatus, a terminal device in a future 5G network, or a terminaldevice in a future evolved PLMN network.

In the embodiments of the present invention, a network device may be adevice configured to communicate with user equipment. The network devicemay be a base transceiver station (Base Transceiver Station, “BTS” forshort) in a GSM system or CDMA, may be a NodeB (NodeB, “NB” for short)in a WCDMA system, or may be an evolved NodeB (Evolutional Node B, “eNB”or “eNodeB” for short) in an LTE system. Alternatively, the networkdevice may be a relay station, an access point, an in-vehicle device, awearable device, a network device in a future 5G network, a networkdevice in a future evolved PLMN network, or the like.

FIG. 1(a) and FIG. 1(b) are application scenario diagrams according toan embodiment of the present invention. As shown in FIG. 1(a) and FIG.1(b), an SGs interface is established between a mobility managemententity (Mobility Management Entity, “MME” for short) and a mobileswitching center (Mobile Switching Center, “MSC” for short), toassociate an LTE network with a 3G/2G network.

A terminal device supports circuit switched fallback (Circuit SwitchedFallback, “CSFB” for short). When the terminal device is switched on,the terminal device is registered with both the LTE network and the2G/3G network, and preferentially camps on the LTE network. As shown inFIG. 1(a), when the terminal device needs to initiate paging, theterminal device initiates a voice service request to the MME. The MMEinstructs the terminal device to fall back to the 2G/3G network. Theterminal device falls back to the 2G/3G network according to theinstruction from the MME, and makes a mobile originating call (MobileOrigination Call, “MO” for short) in the 2G/3G network according to anormal procedure. As shown in FIG. 1 (b), after the MME receives apaging message that is sent by the MSC by using the SGs interface, theMME pages the terminal device and instructs the terminal device to fallback to the 2G/3G network. After falling back to the 2G/3G networkaccording to the instruction from the MME, the terminal device completesa called connection according to a normal procedure.

After completing a voice call, the terminal device returns to the LTEnetwork for camp-on.

FIG. 2 is a schematic flowchart of a voice service processing methodaccording to an embodiment of the present invention. As shown in FIG. 2,the method 100 includes the following steps.

S110. A terminal device sends a circuit switched fallback CSFB requestto a network device.

The terminal device accesses a 4G LTE network. When a user needs to makea call or answer a call, the terminal device sends the CSFB request tothe network device, to request to fall back to a 2G or 3G network.

S120. The network device delivers a radio resource control RRCconnection release (Release) message to the terminal device.

Generally, the RRC release message carries a release reason (forexample, other (other)), a redirection standard, and redirectionfrequency information. However, sometimes, due to an exception on anetwork side, the RRC release message carries only the release reason,but carries no redirection standard and redirection frequency.

S130. The terminal device determines whether the RRC release messagecarries frequency information.

Optionally, in S130, if the RRC release message carries frequencyinformation, the terminal device scans 2G/3G frequencies indicated bythe frequency information, to receive receiving strength of thefrequencies; sorts, according to receiving strength, frequenciesdelivered by the network, where stronger strength indicates a higherpriority; performs a synchronization operation on frequencies with ahighest priority according to priorities; and receives a system messageafter the synchronization succeeds. If an access condition is currentlymet, and a location area of a 2G/3G frequency is the same as a locationarea of a frequency delivered by the network to the terminal deviceduring LTE attach, the terminal does not perform a registrationoperation, but directly performs a subsequent call operation in 2G/3G Ifan access condition is currently met, but a location area of a 2G/3Gfrequency is different from a location area delivered by the network tothe terminal device during LTE attach, the terminal device performs alocation area update (Location Area Update, “LAU” for short) operationon a fallback frequency, performs a subsequent call operation afterfallback succeeds, and fast returns (Fast Return, “FR” for short) to 4Gafter a call is ended.

Optionally, in S130, if the RRC release message received by the terminaldevice carries no frequency information, according to an existing CSFBsolution, the terminal device considers that the received RRC releasemessage is used to instruct the terminal device to release an RRCconnection. Then, the terminal device releases an RRC connection to theLTE network. In addition, the terminal device cannot obtain a frequencythat is to be used during fallback. Therefore, the terminal devicecannot fall back to the 2G/3G network from the LTE network.Consequently, a mobile originating/terminating call of the terminaldevice is disconnected. However, in this embodiment of the presentinvention, if the RRC release message received by the terminal devicecarries no frequency information, the terminal device may perform S140and steps subsequent to S140, to implement fallback from the LTE networkto the 2G/3G network.

S140. If the RRC connection release message carries no frequencyinformation, the terminal device queries whether a current procedure isa CSFB procedure.

Inside the terminal device, an LTE RRC layer may query an LTE non-accessstratum (Non Access Stratum, “NAS” for short) about whether the currentprocedure is a CSFB procedure. Specifically, the RRC layer querieswhether the LTE NAS (“LNAS” for short) has sent an extend servicerequest (Extend Service Request, “ESR” for short) message to the LTEnetwork and a service type (Service Type) in the ESR message, todetermine whether the current procedure is a CSFB procedure. If the RRClayer finds that the LANS has sent no ESR message to the LTE network, orthe LNAS has sent an ESR message to the network, but a service type inthe ESR message is neither mobile-originating-CSFB(Mobile-originating-CS-fallback) nor mobile-terminating-CSFB(Mobile-terminating-CS-fallback), the RRC layer determines that thecurrent procedure is not a CSFB procedure. If the RRC layer finds thatthe LNAS has sent an ESR message to the network, and a service type inthe ESR message is either Mobile-originating-CS-fallback orMobile-terminating-CS-fallback, the RRC layer determines that thecurrent procedure is a CSFB procedure.

S150. The terminal device determines that the current procedure is aCSFB procedure, and the terminal device obtains historical frequencies.

If the network device delivers no frequency that can be used by theterminal device during fallback, the terminal device may obtain thehistorical frequencies, and determine an available frequency from thehistorical frequencies according to a prior-art procedure, and then fallback to the 2G/3G network by using the frequency, to make a call oranswer a call.

In this embodiment of the present invention, optionally, the historicalfrequencies may be saved by the terminal device. Specifically, as shownin FIG. 3, the method 100 further includes the following steps.

S160. The terminal device saves a relationship between 4G and a 2G/3Gfrequency.

Specifically, when the received RRC release message delivered by thenetwork device carries a 2G/3G frequency, the terminal device may save acorrespondence between 4G and the 2G/3G frequency. Alternatively, aftereach time the terminal device successfully falls back to 2G/3G from 4Gthe terminal device may save a correspondence between 4G and a 2G/3Gfrequency used during this fallback. For example, the correspondencebetween 4G and a 2G/3G frequency may be saved in a CSFB experiencetable.

Correspondingly, S150 is specifically: determining whether thecorrespondence between 4G and a 2G/3G frequency exists in the CSFBexperience table.

Therefore, when the terminal device receives no frequency informationdelivered by the network device, the terminal device may directly obtainthe historical frequencies from relationships that are between 4G and a2G/3G frequency and that are saved by the terminal device, and use anappropriate frequency to perform fallback, to ensure a normal call.

It should be noted that sequence numbers of the foregoing procedures donot necessarily represent an execution sequence of the procedures. Forexample, S160 is performed before S150. A specific execution sequence isreflected by a logical relationship between steps.

Optionally, for example, the terminal device may save the relationshipbetween 4G and a 2G/3G frequency in a manner shown in Table 1. Forexample, Table 1 shows information that is saved by the terminal devicewhen a location area identity (Location Area Identification, “LAI” forshort), that is, 1234, is corresponding to a plurality of 3Gfrequencies.

TABLE 1 Mobile country Redirect code-mobile radio access Frequency Indexnetwork code technology band Frequency (Index) (MCC-MNC) LAI (RedirectRAT) (BAND) (Freq) 1 460-01 1234 3G . . . 10713 . . . . . . . . . . . .. . . . . . 2 460-00 . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .

Further, the terminal device may save information according to an arearange of the terminal device. Alternatively, the terminal device maysave, in different relationship tables, correspondences that are between4G and a 2G/3G frequency and that are corresponding to different areas.Therefore, when entering an area, the terminal device may quickly obtaina frequency that is to be used during fallback, so as to reduce timeconsumed for fallback.

In this embodiment of the present invention, optionally, when theterminal device enters an area range, the terminal device may delete acorrespondence that is between 4G and a 2G/3G frequency and that ispreviously saved in another area range, to save internal storage spaceof the terminal.

In this embodiment of the present invention, optionally, the historicalfrequencies obtained by the terminal device may be frequencies that areused to access the 2G/3G network by another terminal device in a processin which the another terminal device is handed over from the 4G networkto the 2G/3G network, and preferably, may be frequencies that are usedto access the 2G/3G network by another terminal device during networkhandover, where a location area of the another terminal device in theprocess in which the another terminal device is handed over from the 4Gnetwork to the 2G/3G network is the same as a current location area ofthe terminal device. In addition, relationships that are between 4G anda 2G/3G frequency and that are corresponding to different terminaldevices in different areas may be saved by using cloud knowledge bases.When the terminal device enters a corresponding area, a cloud server maydeliver, to the terminal device, a cloud knowledge base corresponding tothe area, and the terminal device may directly obtain, from the cloudknowledge base, a frequency that is to be used during fallback. Forexample, when the terminal device is moved from Shanghai to Shenzhen,the terminal device may directly receive a relationship that is between4G and a 2G/3G frequency, that is saved by the cloud server when anotherterminal device is in Shenzhen, and that is delivered by the cloudserver. When the terminal device needs to be handed over from the 4Gnetwork to the 2G/3G network, but receives no frequency delivered by thenetwork device, the terminal device may directly obtain, from thereceived relationship between 4G and a 2G/3G frequency, a frequency thatcan be used during fallback. Therefore, the terminal device can moreeasily obtain the frequency that is to be used during fallback.

Optionally, location areas may be divided on a basis of a country, acity, an LAI, or the like. This is not limited in the present invention.

In this embodiment of the present invention, optionally, as shown inFIG. 2 and FIG. 3, if the RRC release message carries no frequencyinformation, and the terminal device obtains no historical frequency,the terminal device may perform procedures in S170 and S180.

S170. The terminal device obtains a frequency from a frequency bandsupported by 2G/3G.

Preferably, the terminal device may select a first frequency fromfrequencies supported by 2G/3G.

S180. The terminal device constructs a message that carries thefrequency.

That is, if the terminal device receives no 2G/3G frequency delivered bythe network device, and fails to obtain a historical frequency, theterminal device may perform full frequency band search on the frequencyband supported by the 2G/3G network, and select a frequency from thefrequency band, to make a call or answer a call.

For example, the terminal device may first select the first frequencyfrom the frequency band supported by 2G/3G For example, a firstfrequency in a 2G GSM system is 890.2 MHz. Then, the terminal deviceinternally constructs a message that carries the first frequency. If theterminal device can find the first frequency, the terminal deviceaccesses the 2G network by using the first frequency, to make a call oranswer a call. If the terminal device fails to find the first frequency,the terminal device performs full frequency band search on a frequencyband supported by the 2G network, and determines, according to a searchresult, a frequency that is to be used to access the 2G network.

Further, if the terminal device receives frequency information deliveredby the network device, and the terminal device also obtains frequenciessaved by the terminal device and frequencies that are previously used byanother terminal device during fallback, the terminal device maypreferentially determine, from frequencies indicated by the frequencyinformation, a frequency that is to be used during fallback. If theterminal device fails to determine, from the frequencies indicated bythe frequency information, a frequency that is to be used duringfallback, the terminal device determines, from the frequencies saved bythe terminal device, a frequency that is to be used during fallback. Ifthe terminal device fails to determine, from the frequencies saved bythe terminal device, a frequency that is to be used during fallback, theterminal device further determines, from the frequencies that arepreviously used by the another terminal device during fallback, afrequency that is to be used during fallback. After the foregoingprocedures, if the terminal device still cannot obtain a frequency thatcan be used during fallback, the terminal device may perform fullfrequency band search, to determine a frequency that can be used duringfallback. A method for determining, by the terminal device from aplurality of optional frequencies, a frequency that is to be used duringfallback is the same as a method in a related process in the prior art.Details are not described herein. Therefore, even if the network devicedelivers an incorrect frequency, the terminal device can answer a callor make a call.

In this embodiment of the present invention, optionally, when thehistorical frequencies obtained by the terminal device include both afrequency supported by the 2G network and a frequency supported by the3G network, the terminal device may preferentially fall back to the 2Gnetwork by using the frequency supported by the 2G network.

The voice service processing method according to the embodiments of thepresent invention is described above in detail with reference to FIG. 2and FIG. 3. A terminal device according to an embodiment of the presentinvention is described below in detail with reference to FIG. 4. Asshown in FIG. 4, a terminal device 10 includes a transceiver unit 11 anda determining unit 12.

The transceiver unit 11 is configured to send a first message to anetwork device of a first network, where the first message is used torequest a circuit switched fallback CSFB voice service.

The transceiver unit 11 is further configured to receive a secondmessage sent by the network device of the first network, where thesecond message is used to instruct the terminal device to performnetwork redirection.

The determining unit 12 is configured to: if the second message carriesno frequency information, determine a redirection frequency, where theredirection frequency is a frequency supported by a second network.

The transceiver unit 11 is further configured to send, based on theredirection frequency, a connection request to a network device of thesecond network, to perform a CS voice service.

Therefore, according to the terminal device in this embodiment of thepresent invention, when the terminal device needs to perform a voiceservice, even if the terminal device receives no frequency informationdelivered by a network, the terminal device can determine an appropriateredirection frequency, and access, based on the redirection frequency, anetwork that supports the voice service, to answer a call or make acall. Therefore, voice communication experience of a user is improved.

In this embodiment of the present invention, optionally, the determiningunit 12 is specifically configured to: obtain first historicalfrequencies, where the first historical frequencies are frequencies thatare used before the determining unit 12 determines the redirectionfrequency and that are used to access the second network by the terminaldevice in a process in which the terminal device is handed over from thefirst network to the second network; and determine one of the firsthistorical frequencies as the redirection frequency.

In this embodiment of the present invention, optionally, the determiningunit 12 is specifically configured to: obtain second historicalfrequencies, where the second historical frequencies are frequenciesthat are used before the determining unit 12 determines the redirectionfrequency and that are used to access the second network by anotherterminal device in a process in which the another terminal device ishanded over from the first network to the second network; and determineone of the second historical frequencies as the redirection frequency.

In this embodiment of the present invention, optionally, a location areaof the another terminal device in the process in which the anotherterminal device is handed over from the first network to the secondnetwork is the same as a current location area of the terminal device.

In this embodiment of the present invention, optionally, the transceiverunit 11 is further configured to receive the second historicalfrequencies sent by a cloud server.

In this embodiment of the present invention, optionally, the determiningunit 12 is further configured to save a correspondence between the firstnetwork and the redirection frequency.

In this embodiment of the present invention, optionally, the firstnetwork is a 4G network, and the second network is a 2G network.

It should be understood that the terminal device 10 herein isimplemented in a form of a function unit. The term “unit” herein mayrefer to an application-specific integrated circuit (ApplicationSpecific Integrated Circuit, “ASIC” for short), an electronic circuit, aprocessor (for example, a shared processor, a dedicated processor, or agroup processor) configured to execute one or more software or firmwareprograms, a memory, a combined logic circuit, and/or another appropriatecomponent that supports the described functions. In an optional example,a person skilled in the art may understand that the terminal device 10may be configured to perform the procedures and/or steps in the method100 in the foregoing method embodiment. To avoid repetition, details arenot described herein again.

As shown in FIG. 5, an embodiment of the present invention furtherprovides a terminal device 100. The terminal device 100 includes aprocessor 101, a memory 102, and a radio frequency (Radio Frequency,“RF” for short) circuit 103. A person skilled in the art may understandthat a structure of the terminal device shown in FIG. 5 constitutes nolimitation on the terminal device. The terminal device may include moreor fewer parts than those shown in the figure, or combine some parts, orsplit some parts, or have different part arrangements.

The radio frequency circuit 103 may also be referred to as atransceiver, and is configured to send a first message to a networkdevice of a first network. The first message is used to request acircuit switched fallback CSFB voice service. The radio frequencycircuit 103 is further configured to receive a second message sent bythe network device of the first network. The second message is used toinstruct the terminal device to perform network redirection. Theprocessor 101 is configured to: if the second message carries nofrequency information, determine a redirection frequency. Theredirection frequency is a frequency supported by a second network. Theradio frequency circuit 103 is further configured to send, based on theredirection frequency, a connection request to a network device of thesecond network, to perform a CS voice service.

Therefore, according to the terminal device in this embodiment of thepresent invention, when the terminal device needs to perform a voiceservice, even if the terminal device receives no frequency informationdelivered by a network, the terminal device can determine an appropriateredirection frequency, and access, based on the redirection frequency, anetwork that supports the voice service, to answer a call or make acall. Therefore, voice communication experience of a user is improved.

It should be understood that in this embodiment of the presentinvention, the processor 101 may be a central processing unit (CentralProcessing Unit, “CPU” for short), or the processor 101 may be anothergeneral-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field programmablegate array (FPGA) or another programmable logic device, a discrete gate,a transistor logic device, a discrete hardware component, or the like.The general-purpose processor may be a microprocessor, or the processormay be any conventional processor or the like.

The memory 102 may be configured to store a software program and amodule. The processor 101 runs the software program and the module thatare stored in the memory 102, to execute various function applicationsof the terminal device 100 and process data. The memory 102 may mainlyinclude a program storage area and a data storage area. The programstorage area may store an operating system, an application programrequired by at least one function (such as a sound play function or animage play function), and the like. The data storage area may store data(such as audio data or a phone book) created according to use of theterminal device 100, and the like. In addition, the memory 102 mayinclude a high-speed random access memory, or may include a nonvolatilememory, such as at least one magnetic disk storage device, a flashmemory device, or another volatile solid-state storage device.

The RF circuit 103 may be configured to: receive and send a signal in aninformation receiving or sending process or a call process, and inparticular, after receiving downlink information of a base station, sendthe downlink information to the processor 101 for processing; and senddesigned uplink data to the base station. Generally, the RF circuit 103includes but is not limited to an antenna, at least one amplifier, atransceiver, a coupler, a low noise amplifier (Low Noise Amplifier,“LNA” for short), a duplexer, or the like. In addition, the RF circuit103 may communicate with a network and another device by means ofwireless communication. The wireless communication may use anycommunications standard or protocol, including but not limited to GSM,GPRS, CDMA, WCDMA, LTE, an email, a short message service (ShortMessaging Service, “SMS” for short), and the like.

In an implementation process, the steps in the foregoing method may becompleted by using an integrated logic circuit of hardware in theprocessor 101 or an instruction in a form of software. The steps of themethod disclosed with reference to the embodiments of the presentinvention may be directly performed and completed by a hardwareprocessor, or may be performed and completed by using a combination ofhardware and software modules in the processor. The software module maybe located in a mature storage medium in the field, such as a randomaccess memory, a flash memory, a read-only memory, a programmableread-only memory, an electrically-erasable programmable memory, or aregister. The storage medium is located in the memory 102. The processor101 reads information in the memory 102, and completes the steps of theforegoing method in combination with hardware of the processor. To avoidrepetition, details are not described herein again.

Optionally, in an embodiment, the processor 101 is specificallyconfigured to: obtain first historical frequencies, where the firsthistorical frequencies are frequencies that are used before theprocessor 101 determines the redirection frequency and that are used toaccess the second network by the terminal device in a process in whichthe terminal device is handed over from the first network to the secondnetwork; and determine one of the first historical frequencies as theredirection frequency.

Optionally, in an embodiment, the processor 101 is specificallyconfigured to: obtain second historical frequencies, where the secondhistorical frequencies are frequencies that are used before theprocessor 101 determines the redirection frequency and that are used toaccess the second network by another terminal device in a process inwhich the another terminal device is handed over from the first networkto the second network; and determine one of the second historicalfrequencies as the redirection frequency.

Optionally, in an embodiment, a location area of the another terminaldevice in the process in which the another terminal device is handedover from the first network to the second network is the same as acurrent location area of the terminal device.

Optionally, in an embodiment, the RF circuit 103 is further configuredto receive the second historical frequencies sent by a cloud server.

Optionally, in an embodiment, the memory 102 is configured to save acorrespondence between the first network and the redirection frequency.

Optionally, in an embodiment, the first network is a 4G network, and thesecond network is a 2G network.

It should be understood that the terminal device 100 according to thisembodiment of the present invention may be corresponding to the terminaldevice 10 in the embodiments of the present invention, and may becorresponding to the terminal device that performs the method 100according to the embodiments of the present invention, and the foregoingand other operations and/or functions of the modules in the terminaldevice 100 are separately intended to implement procedures correspondingto the terminal device in the method in FIG. 2 and FIG. 3. For brevity,details are not described herein again.

Therefore, according to the terminal device in this embodiment of thepresent invention, when the terminal device needs to perform a voiceservice, even if the terminal device receives no frequency informationdelivered by a network, the terminal device can determine an appropriateredirection frequency, and access, based on the redirection frequency, anetwork that supports the voice service, to answer a call or make acall. Therefore, voice communication experience of a user is improved.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of the present invention.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiment, and detailsare not described herein again.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiments are merely examples. For example, the unit division ismerely logical function division and may be other division during actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,that is, may be located in one position, or may be distributed on aplurality of network units. Some or all of the units may be selectedaccording to actual requirements to achieve the objectives of thesolutions of the embodiments.

In addition, function units in the embodiments of the present inventionmay be integrated into one processing unit, or each of the units mayexist alone physically, or two or more units are integrated into oneunit.

When the functions are implemented in the form of a software functionunit and sold or used as an independent product, the functions may bestored in a computer readable storage medium. Based on such anunderstanding, the technical solutions in the present inventionessentially, or the part contributing to the prior art, or some of thetechnical solutions may be implemented in a form of a software product.The computer software product is stored in a storage medium, andincludes several instructions for instructing a computer device (whichmay be a personal computer, a server, a network device, or the like) toperform all or some of the steps of the methods described in theembodiments of the present invention. The foregoing storage mediumincludes: any medium that can store program code, such as a USB flashdrive, a removable hard disk, a read-only memory (ROM, Read-OnlyMemory), a random access memory (RAM, Random Access Memory), a magneticdisk, or an optical disc.

The foregoing descriptions are merely specific implementations of thepresent invention, but are not intended to limit the protection scope ofthe present invention. Any variation or replacement readily figured outby a person skilled in the art within the technical scope disclosed inthe present invention shall fall within the protection scope of thepresent invention. Therefore, the protection scope of the presentinvention shall be subject to the protection scope of the claims.

What is claimed is:
 1. A voice service processing method, wherein themethod comprises: sending, by a terminal device, a first message to anetwork device of a first network, wherein the first message requests acircuit switched fallback (CSFB) voice service; receiving, by theterminal device, a second message sent by the network device of thefirst network, wherein the second message instructs the terminal deviceto perform network redirection; with the second message carrying nofrequency information of a second network for the network redirection,determining, by the terminal device, a redirection frequency, whereinthe redirection frequency is a frequency supported by the secondnetwork, and internally constructing, by the terminal device, a messagethat carries the redirection frequency; and sending, by the terminaldevice based on the redirection frequency obtained from the internallyconstructed message carrying the redirection frequency, a connectionrequest to a network device of the second network, to perform a circuitswitched (CS) voice services, wherein the determination of theredirection frequency comprises: obtaining, by the terminal device,historical frequencies, wherein the historical frequencies arefrequencies that are used to access the second network by anotherterminal device in a process in which the another terminal device ishanded over from the first network to the second network, and a locationarea of the another terminal device is the same as a current locationarea of the terminal device.
 2. The method according to claim 1, whereinthe determination of the redirection frequency further comprises:determining, by the terminal device, one of the obtained historicalfrequencies as the redirection frequency.
 3. The method according toclaim 2, wherein the location area of the another terminal device is alocation area of the another terminal device in the process in which theanother terminal device is handed over from the first network to thesecond network.
 4. The method according to claim 2, wherein theobtaining, by the terminal device, of the historical frequenciescomprises: receiving, by the terminal device, the historical frequenciessent by a cloud server.
 5. The method according to claim 1, wherein themethod further comprises: saving, by the terminal device, acorrespondence between the first network and the redirection frequency.6. The method according to claim 1, wherein the first network is aFourth Generation Mobile Communications Systems (4G) network, and thesecond network is a Second Generation Mobile Communication Systems (2G)network.
 7. A terminal device, comprising a processor, a memory, and atransceiver, wherein the processor, the memory, and the transceiver areconnected by using a bus system; the memory is configured to storeinstructions; the transceiver is controlled by the processor to receiveand send a message, to implement communication between the terminaldevice and a network device; and the processor is configured to invokethe instructions stored in the memory, to make the terminal deviceperform: sending a first message to a network device of a first network,wherein the first message requests a circuit switched fallback (CSFB)voice service; receiving a second message sent by the network device ofthe first network, wherein the second message instructs the terminaldevice to perform network redirection; with the second message carryingno frequency information of a second network for the networkredirection, determining, by the terminal device, a redirectionfrequency, wherein the redirection frequency is a frequency supported bythe second network, and internally constructing, by the terminal device,a message that carries the redirection frequency, and sending, based onthe redirection frequency obtained from the internally constructedmessage carrying the redirection frequency, a connection request to anetwork device of the second network, to perform a circuit switched (CS)voice service, wherein the determination of the redirection frequencycomprises: obtaining, by the terminal device, historical frequencies,wherein the historical frequencies are frequencies that are used toaccess the second network by another terminal device in a process inwhich the another terminal device is handed over from the first networkto the second networks, and a location area of the another terminaldevice is the same as a current location area of the terminal device. 8.The terminal device according to claim 7, wherein the determination ofthe redirection frequency further comprises: determining, by theterminal device, one of the obtained historical frequencies as theredirection frequency.
 9. The terminal device according to claim 8,wherein the location area of the another terminal device is a locationarea of the another terminal device in the process in which the anotherterminal device is handed over from the first network to the secondnetwork.
 10. The terminal device according to claim 8, wherein theobtaining of the historical frequencies comprises: receiving, by theterminal device, the historical frequencies sent by a cloud server. 11.The terminal device according to claim 7, wherein the processor isfurther configured to invoke the instructions to make the terminaldevice perform: saving a correspondence between the first network andthe redirection frequency.
 12. The terminal device according to claim 7,wherein the first network is a Fourth Generation Mobile CommunicationsSystems (4G) network, and the second network is a Second GenerationMobile Communication Systems (2G) network.